added pref to enable session restore by default
added pref to enable session restore by default

bra1nb3am3r/palemoon-tabgroups,JustOff/palemoon-tabgroups,andreieftimie/firefox-tabgroups,wolfbeast/palemoon-tabgroups,wolfbeast/palemoon-tabgroups,bra1nb3am3r/palemoon-tabgroups,bra1nb3am3r/palemoon-tabgroups,JustOff/palemoon-tabgroups,wolfbeast/palemoon-tabgroups,JustOff/palemoon-tabgroups,andreieftimie/firefox-tabgroups